The linearity of some monitors suffers with high
levels because the voice coil moves outside the linear fluxivity region of the magnetic
gap. But at low levels the voice coil stays close to the centre of the gap and so that's
ot a problem...

Conversely, in ported monitors the loading on the bass driver
changes with volume becuae of the acoustic impednace and the momentum of the moving aor
mass inside the enclosure trying to fight its way out of the port(s).

As a
result, ported speakers tend to go bass light as you reduce the listening volume, and this
effect is emphasised by our own non-linear hearing response (as mentioned above).